There are numerous examples within nature which support the theory of evolution by demonstrating change over time
- The fossil record, selective breeding and comparative anatomy are three of the most widely recognised pieces of evidence
- Biogeography, vestigial structures and comparative embryology provide further evidence for evolution
- Additionally, molecular evidence (e.g. gene sequencing) is now being used to demonstrate evolutionary relationships
Vestigial Structures
Some species show the presence of functionless and reduced remnants of organs that were once present in their ancestors
- Changes to the environment have rendered these organs redundant and so over time they have lost their functionality
These structures are called vestigial organs and demonstrate the evolutionary divergence of a species from a past activity
- An example of a vestigial organ is the pelvic bone in whales – this bone suggests that whale ancestors were terrestrial mammals
Example of a Vestigial Structure
Biogeography
Biogeography describes the distribution of lifeforms over geographical areas, both in past and present times
- Related species are usually found in close physical proximity (supporting the concept of speciation via gradual divergence)
- Fossils found in a particular region tend to closely resemble the modern organisms of the region
Biogeography provides evidence for evolution because it suggests that closely distributed species share a common lineage
- If speciation was random, the distribution of structurally similar species would be expected to be scattered
Examples of biogeographical distribution indicating shared ancestry can be observed by the fact that:
- Most modern marsupials are found almost exclusively in Australia (~70% of extant species)
- Australia has few placental mammals compared to South America, even though environmental conditions are similar
Exceptions to this correlation between biogeographical distribution and common ancestry can be explained by continental drift
- Over 250 million years ago, there was a single continental landmass (Pangaea) which split into the 6 current land regions
- Closely related species that were separated by the breaking landmass are localised to regions that were once connected
- For example, ratites (flightless birds) are distributed globally according to regions that were once part of Gondwanaland
Biogeographical Distribution of Ratites as Explained by Continental Drift
Comparative Embryology
Studying the growing embryo in animals or plants shows that closely related species go through similar stages of development
- These similarities in embryonic development suggest that the organisms shared a common evolutionary pathway
Comparing the embryonic development of a range of diverse animal species, it can be seen that:
- All terrestrial animals have non-functioning gill slits (pharyngeal slits) as early embryos (suggesting an aquatic origin)
- Many vertebrates (including humans) demonstrate a primitive tail at an early stage of embryonic development
Guess the Embryo!
⇒ Click on the diagram to show the answers